1. Field of the Invention
The present invention relates in general to a cam driving apparatus for a Stirling cycle module, and in particular to a cam driving apparatus in which a circumferential surface thereof is equipped with an upper cam curve portion and a lower cam curve portion thus achieving a light and compact cam module driving apparatus.
2. Description of the Conventional Art
Referring to FIG. 1 and FIG. 2, there is shown a conventional cam driving apparatus for a Stirling cycle module. A displacer 1 is disposed at an inside upper portion of a cylinder(not shown) in order to control an active gas in a cylinder. A piston 2 is disposed below the displacer 1 and operated in a different cycle from the displacer 1 in order to control the active gas in a cylinder. Here, a cam driving section 30 includes a rotary cylindrical cam 7 and a plurality of displacer connecting rod bearings 8 and a plurality of piston connecting rod bearings 8'. The cylindrical cam 7 has a peripheral cam groove 12 formed therein with a two-cycle sine curve configuration and is disposed below the piston 2. Here, the bottom portion of the displacer 1 is connected with the upper end of a displacer connecting rod 4 from a lower end of which depend a pair of displacer connecting rod forks 4a and 4b and the lower ends thereof are each equipped with the displacer connecting rod bearings 8. The displacer connecting rod bearings 8 are slidably engaged into the cam groove 12. The piston is centrally formed with a through bore hole 2' which is slidable along the connecting rod 4 of the displacer 1. The bottom surface of the piston 2 is connected with the upper ends of two piston connecting rods 3 and the lower ends of both piston connecting rod 3 are equipped with the piston connecting rod bearings 8', respectively. The piston connecting rod bearings 8' are slidably engaged into the cam groove 12. Here, the displacer connecting bearings 8 and the piston connecting rod bearings 8' are separated circumferentially from each other along the cam groove 12 in order to avoid interfering with one another while running along the cam groove 12.
Meanwhile, the piston 2 and the cam driving section 30 are divided from each other by a guide plate 5. Here, the guide plate 5 has a displacer connecting rod guiding opening 6' formed centrally therethrough in order to guide a vertical movement of the displacer connecting rod 4. In addition, a plurality of piston connecting rod guiding openings 5b are formed at predetermined portions of the guide plate 5 in order to guide a vertical movement of the piston connecting rods 3.
The operation of the conventional cam driving apparatus for a Stirling cycle module will now be described with reference to FIG. 1 and FIG. 2.
To begin with, the displacer connecting rod bearings 8 and the piston connecting rod bearings 8' which are slidably engaged into the cam groove 12 run along a two-cycle sine curve portion, formed in the circumferencial surface, of the cam groove 12 as the cylindrical cam 7 rotates. The displacer connecting rod 4 and integral forks 4a and 4b equipped with the displacer connecting rod bearings 8 at both ends thereof vertically reciprocates in the cam groove and therefore the displacer 1 vertically reciprocates in the cylinder. Meanwhile, the piston connecting rods 3 equipped with the piston connecting rod bearings 8' at the lower ends thereof vertically reciprocate in the cam groove 12 and therefore the piston 2 vertically reciprocates in the cylinder in a different cycle from the displacer 1. While the displacer 1 and the piston 2 run as aforementioned, vibration occurs therein due to a high speed rotation of the cam. For preventing the vibration at the displacer connecting rod 4, there is formed the displacer connecting rod guiding opening 6' in the center portion of the guide plate 5 and for preventing the vibration at the piston connecting rods 3, there are formed the plurality of piston connecting rod guiding openings 5a and 5b in the guide plate 5.
In the aforementioned structure of the conventional Stirling cycle module driving apparatus, if it is attempted to downsize the Stirling module by decreasing the diameter of the cylindrical cam 7, the displacer connecting rod bearings 8 disposed at predetermined distances from the piston connecting rod bearings 8' interfere with one another during running along the cam groove 12. In addition, if in order to resolve the problem, if the diameter of the cylindrical cam 7 is increased, thereafter the size of the cylinder become increased, and thus the circumferential rotation speed of the cylindrical cam 7 becomes slow, so that it is difficult to make the size of the cylindrical cam smaller. Otherwise, it is required to make the pans of the Stirling cycle module cam driving apparatus able to cope with the high speed for a predetermined rotation speed of the cylindrical cam, which makes the cost too high.